Low frequency triangular waveform generator



LOW FREQUENCY TRIANGULAR WAVEFORM GENERATOR Joseph F. Brunihaugh,Niagara Falls, and Allen H. Retzlafi, Locliport, N. Y., assignors to theUnited States of America as represented by the Secretary of the Air Itis the object of this invention to provide a triangular waveformgenerator having a period of the order of 6 to seconds and a waveform ofgood linearity. The invention will be fully described in connection witha preferred embodiment thereof shown in the accompanying drawings, inwhich Fig. l is a schematic circuit diagram of the triangular waveformgenerator; and

Fig. 2 shows a set of waveforms occurring at various places in thecircuit of Fig. 1;'

Referring to Fig. l, pentode tube V1 and its associated circuitconstitute the triangularwave generator, the cathode follower stage V2being only for the purpose of isolating the generator from its loadcircuit. The triangular voltage wave is generated across condenser C1,or across C2 or C3 depending upon the position of switch S1. The fallingportion of this wave, designated m in Fig. 2, is generated by thecharging of C1 from voltage source E1 through resistors R7 and R8 andthe control grid cathode path of V1; the rising portion, designated n inFig. 2, is generated by the discharge of C1 through the anode-cathodepath of V1 and resistor R9. The manner in which the circuit oscillatesbetween these two conditions is as follows:

Assume voltages E1 and E2 to be removed and condenser C1 to be fullydischarged. Upon application of the voltages E1 and E2 at time to, C1begins to charge through R7, R8 and the grid-cathode path of V1 causinga slight rise B in control grid voltage relative to the cathode ofsufficient magnitude to provide a current flow from grid to cathodeequal to the charging current. Since the potential across C1 can notchange instantaneously the anode voltage at to equals the grid voltageand experiences the same slight rise B. Because the anode potential isbelow its cut-off value, there is no anode conduction at this time. Thescreen grid current, however, has its maximum value and this currentflowing through R4 reduces the screen grid voltage to its minimum value.Since the suppressor grid voltage is directly related to the screen gridvoltage through the action of potential divider R3R1-R2, this grid alsohas its minimum voltage at this time.

As C1 charges its voltage increases and the anode potential rises. Thisrise is made linear with respect to time by operating on the linearportion of the charging characteristic. Eventually, at time ti, theanode potential becomes high enough that some of the electrons formerlygoing to the screen grid now pass through the suppressor grid and reachthe anode. The resulting decrease in screen current causes a furtherincrease in screen and suppressor voltages which in turn causes a stillfurther increase in anode current and decrease in screen current. Aregenerative condition therefore exists which produces an almostinstantaneous transition at ti from a condition of zero anode current toa condition in which C1 is discharging through the anode-cathode path ofV1 and resistors Re and R9.

Patent I When anode conduction begins there is an immediate drop inanode potential due to this conduction and an equal drop in gridpotential due to the fact that an immediate change in the voltage acrossC1 is not possible. This equal drop of anode and grid voltages isdesignated A in Fig. 2. At the instant when the control grid potentialfalls below the cathode potential R9 and R6 are introduced into thecharging circuit of C1 since the shunting effect of the grid-cathodepath of tube V1 is removed. The effective charging voltage across C1therefore becomes less than the condenser voltage and as a result C1begins to discharge through V1, Re and R9.

During discharge the grid potential is determined by the dischargecurrent flowing through relatively large resistor R This results in anegative feedback action which holds the discharge current flowingthrough Vi constant thus insuring a linear portion n of the triangularwave.

' As C1 discharges the anode potential falls until eventually thepotential is reduced to the point at which some of the electrons fail topenetrate the suppressor grid and return to the screen grid. Thisincreases the screen current which lowers its potential and also that ofthe suppressor grid due to the coupling between these grids. Thisresults in a still further decrease in anode current and increase inscreen current so that a regenerative situation exists that rapidly cutsofi anode conduction in V1. This event, at t2, marks the end of thecycle. Condenser C1 now begins to recharge through R7, R and the controlgrid-cathode path of V1 starting a new cycle of operation.

Resistor R7 is made variable in order to provide a control over thecharging rate of the capacitor and to permit it to be made equal to thedischarge rate through the tube. Resistor R is a stability control whichestablishes the limit of bias on the suppressor grid and can also beadjusted to compensate for diiferences in individual tubes. With theparameters shown in Fig. 1, the period of the triangular wave withcondenser C1 is about 6 seconds, with C about 8 seconds and with C3about 10 seconds.

We claim:

A low frequency triangular wave generator comprising: a vacuum tubehaving a cathode, a control grid, 9. screen grid, a suppressor grid andan anode; a condenser having one terminal directly connected to saidanode and the other terminal directly connected to said control grid; asource of direct current having positive and negative terminals; meansdirectly connecting said cathode to a point on said source between saidpositive and negative terminals; a resistance connected between saidanode and the positive terminal of said source; a first potentialdivider connected between said positive terminal and said cathode; aresistance connected between said control grid and an intermediate pointon said first potential divider; a'second potential divider connectedbetween said positive and negative terminals; a direct connectionbetween said screen grid and a point on said second potential dividerhaving lower potential than said positive terminal; a direct connectionbetween said suppressor grid and a point on said second potentialdivider located between the point of connection of said screen grid andsaid negative terminal; and an output circuit connected to said controlgrid and said anode.

References Cited in the file of this patent UNITED STATES PATENTSJohnson Feb. 5, 1952

